A hybrid vehicle having an engine and an electric motor as a drive power source device is arranged such that a rotor shaft of the electric motor is spline-coupled to a suitable drive shaft. Patent Document 1 discloses an example of this arrangement wherein a drive shaft 18 is spline-coupled to a rotor shaft 17 of a motor 12 (electric motor). This Patent Document 1 also discloses an arrangement wherein an engine is operatively connected to a counter shaft 20 radially spaced from a rotary axis of the engine, and the motor 12 is operatively connected to the counter shaft 20 radially spaced from the axis of the motor 12, through the rotor shaft 17 and the drive shaft 18. It is noted that the counter shaft 20 is operatively connected to drive wheels through a differential gear device 21.
In the hybrid vehicle arranged as described above, the rotor shaft 17 is in a free state while a torque variation of the engine is transmitted to the drive shaft 18 through the counter shaft 20, particularly when a drive torque Nm of the motor 12 is close to zero. In this free state of the rotor shaft 17, a tooth butting noise is generated due to mutual butting of spline teeth of the rotor shaft 17 and spline teeth of the drive shaft 18 against each other. To overcome this problem, Patent Document 1 proposes to provide an elastic member 70 in the form of an O-ring in a spline-coupling portion between the rotor shaft 17 and the drive shaft 18, for reducing a butting force of the spline teeth, for thereby reducing the tooth butting noise.